The invention is directed to a method for transmission of information via an asynchronous transfer mode (ATM) and, more particularly, to a method for statistically multipexing ATM connections.
A number of connection types are defined for connections via which information is transmitted according to an asynchronous transfer mode (ATM). Connections having strict demands made on the cell delay times are distinguished from connections that do not make strict demands on the cell delay times.
In particular, connections transmitting information with a constant bit rate (CBR) as well as connections transmitting realtime information with variable bit rate (rt-VBR) are included among connections requiring strict cell delay times.
Non-real time VBR connections (rt-VBR) or connections transmitting information with a variable bit rate (available bit rate, ABR) or unspecified bit rate connections (UBR) are included among connections that do not have strict cell delay times.
The information of all five connection types is conducted in ATM cells in common over virtual paths or virtual lines having a predetermined bit rate (bandwidth). In the framework of setting up new connections that make strict demands for cell delay times, it is necessary to calculate the bandwidth that is required for the totality of all connections conducted over a connecting section/connecting line or a virtual path. The calculation of this effective bandwidth is required in order to determine what bandwidth is still free on the common connecting line and what bandwidth is available for the other connection types (nrt-VBR, ABR, UBR). Upon calculation of this effective bandwidth, a determination is then made as to the rate with which the large cell memory offered for the other connection types is allowed to be emptied.
When setting up an ATM connection, the transmitting means must generally inform a higher-ranking control means (call acceptance control) of previously defined parameters. This is required in order to assure the quality of the connection for all subscribers (quality of service). When, for example, too many cells are transmitted and, thus, the transmission capacity is exceeded, too many cells must be discarded. This, however, must be avoided under all circumstances since this always involves a loss of information. The requirement for a cell loss probability of 10xe2x88x9210 of a connection exists, for example, to achieve this purpose by standardization entities. For this reason, a calculation is already carried out at the connection setup as to whether this new connection can be accepted in addition to already existing connections. When the transmission capacity has already been exhausted, the requested connection is rejected.
A number of transmission parameters are defined for describing these events. These include, for example, the peak cell rate (PCR) defined on a connection. The peak cell rate is an upper limit for the number of ATM cells that can be transmitted per second via this connection. Further transmitting means informs the control means of a sustainable cell rate (SCR) given a connection with variable bit rate. This is the upper limit of an average cell rate with which the cells are transmitted during the existence of the connection. As further parameters, the maximum possible transmission capacity of the connecting line (link cell rate, C) as well as the maximum possible load on the connecting line (p0) are known to the control means. The former is a matter of a quasi-material constant of the connecting line, whereas the latter defines a quantity of the maximum permitted sum cell rate on the connecting line. This is usually 95% of the maximum possible transmission capacity of the connecting line. Based on the measure of these parameters, a decision is then made as to whether new connection requests can be accepted or not.
A number of methods have been developed in the prior art for handling these events. An example of a simple method is the sigma rule algorithm disclosed in detail in German Patent Application DP 19649646.7. The sigma rule algorithm makes a decision at the beginning of a connection setup regarding which of two classes the potentially newly added ATM connection is to be assigned to, namely a class S and a class P. The class S has all virtual connections allocated to it for which a statistical multiplexing according to the sigma rule algorithm would yield a clear gain. These are usually low bit rate connections. The following condition must be met as criterion for these types of connections for the peak cell rate PCR and the sustainable cell rate SCR of all connections to be statistically multiplexed:
(PCR/C less than 0.03) and (0.1xe2x89xa6SCR/PCRxe2x89xa60.5)
All other virtual connections are allocated to the class P. These particularly include connections having constant bit rate. Further, all the connections for which the parameters SCR as well as PCR lie very close to one another or lie very far apart or connections that already exhibit a high peak cell rate PCR are allocated here. A peak cell rate that is greater than 3% of the maximum possible transmission capacity of the connecting line is a valid criterion for this.
The first class S in this prior art is then divided into further sub-classes S1, S2 or S3 in order to achieve an even finer classification. The sigma rule algorithm must, when a new connection request arrives, check which of the sub-classes this new connection is to be assigned to based on the measure of defined interrogation criteria The most favorable sub-class Sx is then automatically selected. A sub-class Sx is thereby defined via a lower limit or, an upper limit of the peak cell rate PCR as well as of the ratio of the transmission parameters SCR/PCR.
This connection acceptance algorithm according to the prior art is, thus, in the position of deciding whether a prescribed bandwidth, (e,g., the bandwidth of a virtual path or a line) is adequate overall for a group of real time connections or constant bit rate connections. Since such acceptance algorithms supply a yes/no decision as a result of determining whether a connection is to be accepted or not, they are not directly suited for calculating the effective bandwidth for a group of connections.
Fundamentally, the effective bandwidth required for a group of real time connections and constant bit rate connections according to the sigma rule acceptance algorithm could be determined with arbitrary precision on the basis of an iterative approximation method. The problem of this method, however, is that the acceptance algorithm would have to be run repeatedly per connection setup and would thus use far too much processor capacity.
The present invention is based on the feature disclosing a way of how an acceptance algorithm is to be fashioned such that a representative bandwidth for all connections can be calculated in an efficient way.
According to an embodiment of the present invention, a method is provided for statistically multiplexing a plurality of ATM connections. The plurality of connections are conducted via a common connecting line having an overall effective bandwidth reserved for conducting the plurality of ATM connections. The common connecting line also utilizes an acceptance algorithm that decides, based on acceptance criteria and a prescribed bandwidth, whether potential additional connections can be accepted on the common connecting line. In particular, the method includes the steps of first setting the overall effective bandwidth equal to an initial value. Next, the overall effective bandwidth is then determined on a step-by-step basis upon occurrence of at least one of a setup of a connection and a release of a connection. The acceptance algorithm is then started during every step and the overall effective bandwidth is modified by at least one of a first traffic parameter and a second traffic parameter based on at least one of the acceptance criteria.
Particularly advantageous for the invention is that the effective bit rate, proceeding from an initial value, is determined step-by-step with the setup/release of connections in that the acceptance algorithm is started at every step and the effective bandwidth is modified by a first or a second traffic parameter according to the measure of an acceptance criterion. The effective band width is thus estimated rather exactly by the yes/no decision of the acceptance algorithm.
Additional advantages and novel features of the invention will be set forth, in part, in the description that follows and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.